1. Field of the Invention
The present disclosure generally relates to a step impedance resonator filter and, more particularly, to a step impedance resonator filter whose performance can be improved by changing the locations of the tapped lines.
2. Description of the Related Art
Wireless communication technology has changed the way people exchange messages. In order to meet different demands of the users exchanging messages, the wireless transceivers with multiple modes and multiple bandwidths have become the essential components in the communication system. For example, since the wireless communication standards IEEE802.11a and IEEE802.11g operate at the bandwidths of 2.4 GHz and 5.2 GHz respectively, the wireless transceiver must include a band-pass filter in order to operate at both the bandwidths of 2.4 GHz and 5.2 GHz. The band-pass filter is able to form a band-pass effect at each of the frequencies of 2.4 GHz and 5.2 GHz while excluding the signals at any frequency other than the above two frequencies, thereby achieving the multi-bandwidth transmission.
A band-pass filter may be formed by one or more step impedance resonators (SIR). For example, the band-pass filter may include two resonators. Each of the resonators usually has an electrical length of a half or a quarter of the wavelength, and includes a coupled line and a tapped line. The coupled lines of the two resonators are coupled with each other in order to deliver the signals. The tapped lines of the two resonators may be used as a signal input end and a signal output end, respectively.
In general, the magnitude of the insertion loss and the ability to generate the transmission zeros at the desired frequency have been the important indicators in evaluating the performance of the filter. However, the lengths or widths of the coupled lines of the two resonators are often changed to improve the insertion loss of the conventional step impedance resonator filter and to adjust the locations of the transmission zeros of said filter without taking the locations of the tapped lines into consideration. As a result, the insertion loss of the conventional step impedance resonator filter cannot be further reduced, and the transmission zeros cannot be precisely generated at the intended frequencies.
In light of this, it is necessary to provide a novel step impedance resonator filter.